This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Application No. 11(1999)-161354 filed on Jun. 8, 1999, the entire content of which is incorporated herein by reference.
The present invention generally relates to a seat device. More particularly, the present invention pertains to a seat reclining device, particularly well suited for use in an automotive vehicle, for adjusting the angle of the seat back relative to the seat cushion.
Unexamined Published Japanese Patent Application (Kokai) No. H09 (1997)-183327 discloses a reclining mechanism which includes a lower arm secured on the seat cushion member, an upper arm rotatably engaging the lower arm and secured on the seat back member, a locking mechanism which includes a cam and restricts the rotation of the upper and lower arms, and spiral springs disposed between the cam and the lower arm for actuating the lock mechanism to restrict the rotation of the upper arm relative to the lower arm. The spiral springs shown in the known reclining mechanism are arranged so that the winding axes of the springs are separated or different from the reclining device rotation axis.
A spiral spring is typically formed by winding steel wire on a cylindrical tool. In actual devices, a spiral spring is installed and utilized in the following way. The inner end of the steel wire is fixed on a shaft, with the shaft center matching the center of the cylindrical tool. The outer end of the steel wire is hooked on an object which moves along a path at a constant distance from the shaft center. Proportional to the rotation angle of the object, a smoothly increasing or decreasing spring force is obtained. The center of the path is called the dynamic center of the spiral spring. However, when the object moves on a path in which the path center does not match the dynamic center of the spiral spring (i.e., when the object approaches towards or moves away from the dynamic center), the spring is distorted in the radial direction. The spring force thus applied to the object varies irregularly, increasing up to an excessively large level.
The Japanese publication mentioned above shows a reclining device employing three spiral springs. The dynamic center of each spiral spring is disposed apart from the reclining device rotation axis. The inner ends of the spiral springs are secured on projections formed on the lower arm, and the outer ends of the spiral springs are hooked on a cam which rotates on the reclining device rotation axis. Therefor, the outer ends of the spiral springs approach or move away from their dynamic centers when the cam rotates, and large radial direction forces are applied by the each spiral spring to the cam. The radial direction forces in three directions cancel each other and prevent an increase of the friction force on the cam bearing with the shaft. However, this configuration requires three spiral springs and makes the reclining device relatively complicated and expensive.
In light of the foregoing, a need exists for a vehicle seat reclining device that is not as susceptible to the disadvantages and drawbacks discussed above.
A need thus exists for a vehicle seat reclining device which does not produce excessive rotation friction during operation of the device, yet which is relatively simple in construction and not excessively expensive.
According to one aspect of the invention, a seat reclining device for a vehicle includes a lower arm adapted to be fixedly arranged on a seat cushion member, an upper arm rotatably arranged with respect to the lower arm and adapted to be fixed on a seat back member, and a locking mechanism for locking the upper arm relative to the lower arm. The locking mechanism includes a rotatable cam and a spring. The spring is disposed between the lower arm and the cam to apply a biasing force to the cam. The spring is disposed so as to be wound around the rotational axis of the cam.
The lower arm is preferably provided with a first recessed portion containing the lock mechanism and a second recessed portion containing the spring, with both of the recessed portions being formed in series along the rotation axis of the cam.
According to another aspect of the present invention, a vehicle seat reclining device includes a lower arm adapted to be fixedly arranged on a seat cushion member, and an upper arm adapted to be fixed on a seat back member, with the upper arm being rotatable relative to the lower arm. A locking mechanism is adapted to lock the upper arm relative to the lower arm and includes a rotatable cam that is rotatable about a rotational axis of the cam. The cam is spring biased by a single spiral spring which applies a biasing force to the cam causing the cam to rotate about the rotational axis of the cam in a direction locking the upper arm relative to the lower arm.
In accordance with another aspect of the invention, a seat reclining device for a vehicle includes a lower arm adapted to be fixedly arranged on a seat cushion member and an upper arm adapted to be fixed on a seat back member, with one of the upper and lower arms being rotatable relative to the other. A locking mechanism locks one of the upper and lower arms relative to the other and includes a rotatable cam that is spring biased by a spiral spring which applies a biasing force to the cam causing the cam to rotate in a direction causing the locking mechanism to effect locking of the upper arm and lower arm relative to one another. The spring includes an inner end which engages a portion of the cam and an outer end which engages one of the upper and lower arms.